1. Field of the Invention
The present invention involves methods, a lubricant composition, and a fuel composition for use in a two-stroke internal combustion engine. The methods and lubricant and fuel compositions are effective in improving the cleanliness of power valves in a two-stroke engine having a variable exhaust timing system.
2. Description of the Related Art
Additives that maintain or improve cleanliness in two-stroke internal combustion engines, especially those equipped with power valves, are essential for the durability and satisfactory performance of the engine.
The overall driving force behind introducing power valves into a two-stroke engine is the customer's desire for more power. The most cost effective way to increase power over the entire rpm range, without major engine modifications and without negatively affecting the excellent power to weight ratio in a two-stroke engine, is to incorporate power valves in a system in which the timing for the exhaust step varies with engine conditions. The power output characteristics of a two-stroke engine are, in part, determined by the location of the top of the exhaust port. A low port height provides an engine with good low-end output, whereas a high port height provides better peak horsepower. The use of a power valve enables the engine to have both characteristics, good low end power with good peak output, by accurately setting the timing for opening and closing the power valve. This timing is established by overlaying the power curves of a low exhaust port and high exhaust port engine design, then finding the “cross-over” RPM where the power curves meet. This is the RPM at which the valves are opened and closed. Power valves are retracted or extended based on engine speed and load by mechanical pressure or electronic servo-motor activated systems. Some of the more sophisticated systems incorporate programmed auto-cleaning cycles and may include control by other engine or external parameters. In order to insure that power valves operate well, carbon build-up and gumming must be inhibited and/or eliminated. Various manufacturers refer to power valves and/or the system to activate them by a variety of names to include exhaust port valves, variable exhaust timing systems, exhaust port modifiers, arctic power valves, variable exhaust valves, variable exhaust systems and rotax adjustable variable exhaust (RAVE).
International Publication No. WO 00/14185 discloses a two-cycle oil and a fuel comprising such an oil where the oil consists of a polyisobutylene amine, a nitrogen-containing dispersant, a polybutene polymer, a solvent, and a lubricating oil and exhibits improved performance and does not contribute to the clogging of variable exhaust systems.
The methods, lubricant composition, and fuel composition of the present invention are unexpectedly effective in inhibiting and/or eliminating carbon buildup, clogging and gumming of power valves. This improved power valve cleanliness is achieved in addition to maintaining and/or improving overall two-cycle engine performance. Test evaluations in a two-stroke engine containing power valves hereinbelow demonstrate the unexpected effectiveness of the present invention.